Percutaneous transluminal coronary angioplasty (PTCA) is used to reduce arterial build-up of cholesterol fats or atherosclerotic plaque. Typically a guidewire is steered through the vascular system to the site of therapy. A guiding catheter, for example, can then be advanced over the guidewire and a balloon catheter advanced within the guiding catheter over the guidewire. The balloon at the distal end of the catheter is inflated causing the site of the stenosis to widen. The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten re-closure of the dilated vessel or even perforations in the vessel wall. Implantation of a metal stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. Reducing the possibility of restenosis after angioplasty reduces the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary.
An implanted prosthesis such as a stent can preclude additional procedures and maintain vascular patency by mechanically supporting dilated vessels to prevent vessel collapse. Stents can also be used to repair aneurysms, to support artificial vessels as liners of vessels or to repair dissections. Stents are suited to the treatment of any body lumen, including the vas deferens, ducts of the gallbladder, prostate gland, trachea, bronchus and liver. The body lumens range in size from the small coronary vessels to the 30 mm aortic vessel. The invention applies to acute and chronic closure or reclosure of body lumens.
A stent typically is a cylindrically shaped device formed from wires or a slotted tube and intended to act as a permanent prosthesis. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration which allows it to contact and support a body lumen. The stent can be made to be radially self-expanding or expandable by the use of an expansion device. The self expanding stent is made from a resilient springy material while the device expandable stent is made from a material which is plastically deformable. A plastically deformable stent can be implanted during a single angioplasty procedure by using a balloon catheter bearing a stent which has been crimped onto the balloon. Stents radially expand as the balloon is inflated, forcing the stent into contact with the body lumen thereby forming a supporting relationship with the vessel walls. Deployment is effected after the stent has been introduced percutaneously, transported transluminally and positioned at a desired location by means of the balloon catheter.
The stainless-steel or tantalum mesh stent that props open blocked coronary arteries, keeps them from reclosing after balloon angioplasty. A balloon of appropriate size and pressure is first used to open the lesion. The process is repeated with a stent crimped on a balloon. The stent is deployed when the balloon is inflated. The stent remains as a permanent scaffold after the balloon is withdrawn.
A number of different stent structures and placement instruments have been developed. For example, Wall in U.S. Pat. No. 5,266,073 describes a rolled tubular stent carried at the end of a tubular catheter with a second catheter threaded therethrough to carry a balloon. The assembly is inserted into an artery until the stent is at the proper location, then the balloon catheter is positioned within the stent and expanded to expand, unroll and lock the stent. This arrangement usually requires an undesirably large diameter catheter for carrying the stent and includes a complex and possibly unreliable locking method for holding the stent in the expanded position. Also, non-uniform stent expansion may occur, since the expanding balloon cannot directly contact the portion of the stent that overlaps its carrier catheter.
Other stent delivery systems have a self-expanding stent compressed in a tube, such as that described by Burton et al. in U.S. Pat. No. 5,026,377. The tube is inserted until the stent is in the desired location and the stent is forced from the tube and expands into contact with the vessel wall. A balloon catheter may be inserted and expanded to further expand the stent. Problems may arise with maintaining the partially expanded stent in position and preventing pushing the stent out of position during insertion of the balloon catheter.
Others have used a rolled tubular stent placed around a balloon catheter and covered by a tubular sheath connected to a guidewire extending through the catheter, such as is described by Lau et al. in U.S. Pat. No. 5,158,548. The assembly is inserted in to a desired location in a body lumen, the sheath is moved longitudinally by the guidewire away from the stent and the balloon is expanded to expand the stent. This requires a complex tubular catheter, sheath and stent assembly.
Balloon catheters are available with a stent preloaded around the balloon. This requires a second balloon catheter to be used to dilate the lesion enough to allow the stent to enter. Subsequently, the catheter bearing the stent is introduced and the stent emplaced. This requires the use of two expensive catheters to complete placement of the stent and two catheterization.
Loose stents are available which users simply slip over a balloon catheter and crimp against the catheter balloon with the fingers. While this arrangement is simple and quick, the stent may be damaged during storage and handling prior to use, while it is being placed over the catheter balloon or during the crimping step. Damaged stents cannot be used. If damage to the stent is not noticed, the stent may not perform as intended in use. Further, depending on the type of delivery system, fitting the stent over the delivery end without damage is sometimes difficult.
Excellent methods and apparatus for mounting stents on catheter balloons and the like are described by Rupp et al. in U.S. patent application Ser. No. 08/576,720, filed Dec. 21, 1995, now pending and assigned to the assignee of this application. While the methods and apparatus described in that application provide excellent results, I have found that in some instances a disposable mounting device is preferable.
Thus, there is a continuing need for improved devices and methods for mounting a stent onto a delivery system such as a balloon catheter that are simpler, less expensive, more convenient, more reliable, avoid damage to the stent and include a sterile, disposable, mounting device to avoid contact between a sterile stent and catheter and a non-sterile surface.